Automatically shiftable vehicle transmissions in planetary design have been described multiple times in the state of the art and are undergoing continuous further development and improvement. The objective is for these transmissions to exhibit an adequate number of gears and a gear ratio suitable for motor vehicles, with a high overall transmission ratio spread, favorable gear steps and a launching torque ratio that is sufficiently high for the specific application. At the same time, the construction expenditure of these transmissions should be as low as possible; particularly, only a small number of shift elements should be required. In addition, in sequential shifting mode, grouped shifting is generally avoided; i.e. when shifting into the next higher or the next lower gear, only one previously engaged shift element is disengaged and one previously disengaged shift element is engaged.
A generic automatic transmission with a transmission housing, an input shaft, an output shaft, four planetary gear sets, two hydraulically actuatable brakes and four hydraulically actuatable clutches, in which three of these six shift elements are engaged in every gear to create one reverse gear and ten shiftable forward gears without grouped shifting, is known from US 2016/0160964 A1. The first two of the four planetary gear sets form an upstream gear set, which is a reduced two connections-four shafts transmission in the design of a Simpson planetary gear set and is permanently connected to the input shaft. The other two of the four planetary gear sets form a main gear set, which is a two connections-five shafts transmission in a design similar to a Simpson planetary gear set and is permanently connected to the input shaft and to the output shaft. Following the nomenclature used in US 2016/0160964 A1, the first brake and the first clutch are permanently connected only to the main gear set, while the second and the third clutch and the fourth clutch are permanently connected to both the main gear set and the upstream gear set, such that the second, third and fourth clutch are disposed in the power flow between the upstream gear set and main gear set. The second brake is permanently connected only to the upstream gear set. This allows three different output speeds of the upstream gear set, of which one is lower than the input shaft speed, one is equal to the input shaft speed and one is higher than the input shaft speed, to selectively be transmitted to the main gear set. FIG. 1A shows the transmission diagram of this generic automatic transmission; FIG. 1B shows the associated shift logic.
Following the nomenclature of US 2016/0160964 A1, the main gear set includes two individual negative or minus planetary gear sets coupled to one another, each including a sun gear, a ring gear and a planetary gear carrier, on which planetary gears that mesh with said sun gear and said ring gear are rotatably mounted. The two sun gears of the main gear set are permanently connected to one another, form the first shaft of the main gear set, and are permanently connected to the third clutch and the fourth clutch such that the first shaft of the main gear set can optionally be connected to two different elements of the upstream gear set. The planetary gear carrier of the second planetary gear set in the main gear set forms the second shaft of the main gear set, and is permanently connected to the output shaft and to the first clutch. The ring gear of the second planetary gear set in the main gear set forms the third shaft of the main gear set, and is permanently connected to the first brake and the second clutch such that the third shaft of the main gear set can optionally be fixed on the transmission housing or connected to the upstream gear set. The planetary gear carrier of the first planetary gear set in the main gear set forms the fourth shaft of the main gear set, and is permanently connected to the input shaft. The ring gear of the first planetary gear set in the main gear set forms the fifth shaft of the main gear set, and is permanently connected to the first clutch such that the fifth shaft of the main gear set is connectable to the second shaft of the main gear set which forms the output shaft of the transmission.
The upstream gear set of US 2016/0160964 A1 includes two individual negative or minus planetary gear sets coupled to one another, each including a sun gear, a ring gear and a planetary gear carrier, on which planetary gears that mesh with said sun gear and said ring gear are rotatably mounted. The two sun gears of the upstream gear set are permanently connected to one another, form the first shaft of the upstream gear set, and are permanently connected to the first brake, so that the first shaft of the upstream gear set is fixable on the transmission housing. The planetary gear carrier of the first planetary gear set in the upstream gear set forms the second shaft of the upstream gear set and is permanently connected to the input shaft. The ring gear of the first planetary gear set in the upstream gear set and the planetary gear carrier of the second planetary gear set in the upstream gear set are permanently connected to one another, form the third shaft of the upstream gear set, and are permanently connected to the second clutch and the fourth clutch such that the third shaft of the upstream gear set is connectable to the third shaft of the main gear set by engaging the second clutch and to the first shaft of the main gear set by engaging the fourth clutch. The ring gear of the second planetary gear set in the upstream gear set forms the fourth shaft of the upstream gear set, and is permanently connected to the third clutch such that the fourth shaft of the upstream gear set is connectable to the first shaft of the main gear set by engaging the third clutch.